RCrawler101-201605 (Week2)

2016-05-21

Leo Lu

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Outline

Recap for observation skills (10 min)
R Basic (quick recap) and RStudio IDE (10 min)
Connection (20 min)
- Crawler’s toolkits in R
Parsing Data (50 min)
- XPath & CSS
- json
- xml
- html table
- regex
Save your data (10 min)
Case study
References

Recap Observation Skills and HTTP request for Connection

URL, Method, GET, POST, Headers, Body
Excample: PTT Gossiping

R Packages Required

Pipeline Coding

magrittr

Crawler’s toolkits in R

rvest: a web scraper based on httr and xml2
httr: toolkit of HTTP methods in R
XML & : XML parser
xml2: xml parser based on libxml2

misc

stringr: string manipulaiton
data.table: extension of data.frame, a powerful ETL tool in R

Install Packages

(if you haven’t installed those packages yet)

## === install required packages ===
pkg_list <- c("magrittr", "httr", "rvest", "stringr", "data.table",
              "jsonlite", "RSQLite", "devtools")
pkg_new <- pkg_list[!(pkg_list %in% installed.packages()[,"Package"])]
if(length(pkg_new)) install.packages(pkg_new)
if("xmlview" %in% pkg_new) devtools::install_github("hrbrmstr/xmlview")
rm(pkg_new, pkg_list)

Let’s Rock with R!

Must-known keyboard shortcuts

All RStudio keyboard shortcuts

Description	Windows & Linux	Mac
Attempt completion / Indent	`Tab`	`Tab`
Run current line/selection	`Ctrl`+`Enter`	`⌘`+`↩︎`
Comment/uncomment current line/selection	`Ctrl`+`Shift`+`C`	`⌘`+`⇧`+`C`
Reindent lines	`Ctrl`+`I`	`⌘`+`I`
Insert pipe operator	`Ctrl`+`Shift`+`M`	`⌘`+`⇧`+`M`

R recap

How to get help
Working Environment
Basic Data Structure
Function
if/else, for, tryCatch
magrittr
data.table

How to get help

?: Access ducument in R console
??: Search the halp system
google with appropriate keyword. For example:
- R {package name}
- R {algorithm name}
Forum
- Stack Overflow
  A question and answer site for programmers
- Taiwan R user Group
  A free R/data analysis user group in Taiwan
- PTT R_Language board
  A bbs forum for R in Taiwan

Working Environment

Check your working directory everytime you start to work!

Using getwd/setwd to get/set your working directory.

(wd = getwd()) # current config

setwd("resources/img")
getwd()

setwd(wd)

RStudio will set working directory automatically when opening new files.

If you use Projects, RStudio will change working directory for you automatically.

Basic Data Structure

Vector, Matrix, Array, List and Data frame are the most basic data structure in R. These data structures can be mapped into a table according to:

dimension
Homogeneous or Heterogeneous of data type

	Homogeneous	Heterogeneous
1d	Atomic vector	List
2d	Matrix	Data frame
nd	Array

(Atomic) Vector

(Atomic) vector is a basic data structure in R.
They are linear vectors of a single primitive type. A scalar is a vector of length 1.

v1 <- c(1:10)
v1
#>  [1]  1  2  3  4  5  6  7  8  9 10
is.vector(v1)
#> [1] TRUE
length(v1)
#> [1] 10
s1 <- 2
s1
#> [1] 2
is.vector(s1)
#> [1] TRUE
length(s1)
#> [1] 1

List

Lists are also vectors, but not atomic vectors. Lists are generic vectors, with (naturally) different semantics.

Elements in a list can be any kinds type and its length is arbitrary.

Function str can help you investigate the structure of a nested list.

li <- list(a = 1:10, 
           b = c("apple", "banana"))
str(li)

#> List of 2
#>  $ a: int [1:10] 1 2 3 4 5 6 7 8 9 10
#>  $ b: chr [1:2] "apple" "banana"

li2 <- list(li = li, 
            c = matrix(1:4, nrow = 2))
str(li2)

#> List of 2
#>  $ li:List of 2
#>   ..$ a: int [1:10] 1 2 3 4 5 6 7 8 9 10
#>   ..$ b: chr [1:2] "apple" "banana"
#>  $ c : int [1:2, 1:2] 1 2 3 4

Visualising lists

x1 <- list(c(1, 2), c(3, 4))
x2 <- list(list(1, 2), list(3, 4))
x3 <- list(1, list(2, list(3)))

Lists Subsetting

a <- list(a = 1:3, b = "a string", c = pi, d = list(-1, -5))

[ extracts a sub-list. The result will always be a list.

str(a[1:2])
str(a[4])

[[ extracts a single component from a list. It removes a level of hierarchy from the list.

y <- list("a", 1L, 1.5, TRUE)
str(y[[1]])
str(y[[4]])

$ is a shorthand for extracting named elements of a list. It works similarly to [[ except that you don’t need to use quotes.

a$a
a[["b"]]

Lists Subsetting (Pepper Shaker)

Data Frame

Data frame is a 2-dimension data structure to deal with a table-like heterogeneous data.

df <- data.frame(gender = c("male", "female", "female", "male"),
                 age = c(33, 18, 24, 26))
## Add new column in a data frame
df$city <- c("Taipei", "Taipei", "Hsinchu", "Taichung")

df

#>   gender age     city
#> 1   male  33   Taipei
#> 2 female  18   Taipei
#> 3 female  24  Hsinchu
#> 4   male  26 Taichung

str(df)

#> 'data.frame':    4 obs. of  3 variables:
#>  $ gender: Factor w/ 2 levels "female","male": 2 1 1 2
#>  $ age   : num  33 18 24 26
#>  $ city  : chr  "Taipei" "Taipei" "Hsinchu" "Taichung"

Recap: data structure

All data structures above are objects. They apply different methods and saved as different type internally.

object	type	class
c(1, 2.5, 3)	double	numeric
c(“male”, “female”, “female”, “male”)	character	character
factor(c(“male”, “female”, “female”, “male”))	integer	factor
matrix(1:9, nrow = 3)	integer	matrix
list(a = 1:10, b = c(“apple”, “banana”))	list	list
data.frame(a = 1, b = “z”)	list	data.frame

Function

To understand computations in R, two slogans are helpful:

Everything that exists is an object.

Everything that happens is a function call.

John Chambers

`+`
#> function (e1, e2)  .Primitive("+")
`<-`
#> .Primitive("<-")
`[`
#> .Primitive("[")
`c`
#> function (..., recursive = FALSE)  .Primitive("c")

Function in R

A typical function in R may look like:

f <- function(par1, par2, ...) {
    # Some magic happened
    return(sth)    # return something
}

If you don’t use return to specify the return value, the return value will be the last expression inside the function.
Call by value by default
send a copy of a object into a function and the input object won’t change after execution without assignment

If

The basc structure of conditional execution in R is:

if (an expression returns TRUE or FALSE) {
    # do something
} else if (another expression returns TRUE or FALSE) {
    # do something
} else {
    # do something
}

for

Iterate items in R.

# iterate a character vector
for (i in c("a", "b")) {
    print(i)
}

#> [1] "a"
#> [1] "b"

# nested loop
m <- matrix(numeric(), nrow = 2, ncol = 2)
for (i in 1:nrow(m)) {
    for (j in 1:ncol(m)) {
        m[i, j] <- i * j
    }
}
m

#>      [,1] [,2]
#> [1,]    1    2
#> [2,]    2    4

tryCatch

tryCatch let you deal with error handling in R.
Error handling is IMPORTANT when wrapping your crawler into a function because you don’t want your function fail without any outcome.

tryCatch({
  result <- expr
  # If you want to use more than one 
  # R expression in the "try" part then you'll have to 
  # use curly brackets.
  # 'tryCatch()' will return the last evaluated expression 
  # in case the "try" part was completed successfully
}, warning = function(w) {
  message("Here's the original warning message:")
  message(w)
  # Choose a return value in case of warning
  return(NULL)
}, error = function(e) {
  message("Here's the original error message:")
  message(e)
  # Choose a return value in case of error
  return(NA)
},
}, finally {
  message("Some other message at the end")
  # finally:
  # Here goes everything that should be executed at the end,
  # regardless of success or error.
  # If you want more than one expression to be executed, then you 
  # need to wrap them in curly brackets ({...}); otherwise you could
  # just have written 'finally=<expression>' 
})

https://stackoverflow.com/questions/12193779/how-to-write-trycatch-in-r/12195574#12195574

What is magrittr

Pipe argument to right-hand side with %>%

x %>% f is equivalent to f(x)
x %>% f(y) is equivalent to f(x, y)
x %>% f %>% g %>% h is equivalent to h(g(f(x)))
x %>% f(y, .) is equivalent to f(y, x)
x %>% f(y, z = .) is equivalent to f(y, z = x)

Example

library(magrittr)
iris %>% head()

Using the dot place-holder

"Ceci n'est pas une pipe" %>% gsub("une", "un", .)

Workflow of Crawler Design

Architecture of Crawlers

Workflow

找到資料頁，想像資料要長什麼樣子，設想產出的資料格式(schema)
觀察網頁內容，找到資料所在的request/response，再一層層往上解析，套上判斷式及迴圈, 完成爬蟲的自動化。
解析取得的資料。

Crawler’s toolkits in R

rvest: a web scraper based on httr and xml2
httr: toolkit of HTTP methods in R
XML & : XML parser
xml2: xml parser based on libxml2
RCurl: a wrapper of libcurl

HTTP request

A valid HTTP request includes four things:

URL: a unique address for a thing
Method:
- GET: to retrieve a resource
- POST: to create a new resource
Headers: Meta-information about a request
- User-Agent
- Cookie
- Content-type
- List of HTTP header fields
Body: data to be send to a server

Web Connector in R

{httr}
{RCurl}
download.file()
Socket Connection Tools:
- socketConnection
- make.socket / read.socket / close.socket

httr

Basic Features:
- HTTP verbs: GET(), POST(), HEAD()…
- http_status: Translate http status code HTTP status code
- status_code
- set_cookies(): set cookles
- add_headers(): add additional headers to a request.
- headers(): Access response headers
- content(): Retrieve the contents of a request
  - as = “parsed”: detect content type automatically and parse the result
  - as = “text”: return character
  - as = “raw”: return binary

Connection: GET Method

Use GET() to request data from a specific resource

起手式

## Not Run
library(httr)
library(rvest)
res <- GET(
  url = "http://httpbin.org/get",
  add_headers(a = 1, b = 2),
  set_cookies(c = 1, d = 2),
  query = list(q="hihi")
)
content(res, as = "text", encoding = "UTF-8")
content(res, as = "parsed", encoding = "UTF-8")

一個例子學會第一隻爬蟲

PTT Gossiping

library(magrittr)
library(httr)
library(rvest)
#> Loading required package: xml2
url <- "https://www.ptt.cc/bbs/Gossiping/index.html"
res <- GET(url, 
           set_cookies(over18="1"))  # over18 cookie
doc <- res %>% 
  content(as = "text", encoding = "UTF-8") %>% 
  read_html

doc %>% 
  html_nodes(css = ".title a") %>% 
  html_text()
#>  [1] "Re: [新聞] 蔡未完成答卷 兩岸官方溝通喊停"         
#>  [2] "[新聞] 蔡正元今娶馬尾妹　宮廷風婚紗照曝光！"      
#>  [3] "[新聞] 鐵飯碗破了！軍人3年後沒月退俸！"           
#>  [4] "Re: [新聞] 王雪紅發豪語  2020年宏達電要當VR界翹楚"
#>  [5] "[問卦] 要開後宮是不是創立個宗教就好⊙o⊙？"         
#>  [6] "[公告] 八卦板板規(2016.02.16)"                    
#>  [7] "[協尋]行車記錄器-5/14承德路5段與基河路交叉口"     
#>  [8] "Fw: [申請] 發文門檻提高 5/19-5/26"                
#>  [9] "[協尋]行車紀錄器5/19台中-台灣大道與福林路路口"    
#> [10] "[公告] 五月份置底閒聊文"

Cookies

A small piece of data sent from a website and stored in the user’s web browser while the user is browsing it
Someetimes you may need set cookies with set_cookies to retreve a request.

library(httr)
url <- "https://www.ptt.cc/bbs/Gossiping/index.html"
res <- GET(url, 
           set_cookies('over18'='1'))  # over18 cookie

The response status code

url <- "https://www.ptt.cc/bbs/Gossiping/index.html"
res <- GET(url, 
           set_cookies('over18'='1'))  # over18 cookie

# Get an informative description:
http_status(res)
#> $category
#> [1] "Success"
#> 
#> $reason
#> [1] "OK"
#> 
#> $message
#> [1] "Success: (200) OK"

# Or just access the raw code:
res$status_code
#> [1] 200
status_code(res)
#> [1] 200

# highly recommend using one of these functions whenever you're using httr inside a function to make sure you find out about errors as soon as possible.
warn_for_status(res)
stop_for_status(res)

Connection: POST method

Submits data to be processed to a specified resource
The query string (name/value pairs) is sent in the HTTP message body

起手式

## Not Run
library(httr)
library(rvest)
res1 <- POST(url = "http://httpbin.org/post", 
             add_headers(a = 1, b = 2),
             set_cookies(c = 1, d = 2),
             body = "A simple text string or raw vector")

res2 <- POST(url = "http://httpbin.org/post",
             add_headers(a = 1, b = 2),
             set_cookies(c = 1, d = 2),
             body = list(x = "A simple text string", 
                         y = "hihi"))

content(res2, as = "text", encoding = "UTF-8")
content(res2, as = "parsed", encoding = "UTF-8")

一個例子學會第二隻爬蟲: Guestbook

Guestbook

Exercise: Guestbook

Try to post a message in App Engine GuestBook

Let’s see what we got in the
response body

The Response Body

3 ways to access the body of the request:

The Response Body: `httr::content()`

res <- GET("https://www.ptt.cc/bbs/NBA/M.1463302851.A.8D7.html")

binary

(bin <- content(res, "raw")) %>% head(200) # raw (binary) vector
#>   [1] 3c 21 44 4f 43 54 59 50 45 20 68 74 6d 6c 3e 0a 3c 68 74 6d 6c 3e 0a
#>  [24] 09 3c 68 65 61 64 3e 0a 09 09 3c 6d 65 74 61 20 63 68 61 72 73 65 74
#>  [47] 3d 22 75 74 66 2d 38 22 3e 0a 09 09 0a 0a 3c 6d 65 74 61 20 6e 61 6d
#>  [70] 65 3d 22 76 69 65 77 70 6f 72 74 22 20 63 6f 6e 74 65 6e 74 3d 22 77
#>  [93] 69 64 74 68 3d 64 65 76 69 63 65 2d 77 69 64 74 68 2c 20 69 6e 69 74
#> [116] 69 61 6c 2d 73 63 61 6c 65 3d 31 22 3e 0a 0a 3c 74 69 74 6c 65 3e 5b
#> [139] e8 a8 8e e8 ab 96 5d 20 e6 9e 97 e6 9b b8 e8 b1 aa e5 a6 82 e6 9e 9c
#> [162] e5 8a a0 e5 85 a5 e9 a6 ac e5 88 ba e8 83 bd e5 be 97 e5 88 b0 e5 a4
#> [185] 9a e5 b0 91 e4 b8 8a e5 a0 b4 e6 99 82 e9 96 93
# writeBin(bin, "myfile.txt") # the highest fidelity way of saving files to disk

text

content(res, "text", encoding = "UTF-8") %>%  # accesses the body as a character vector
  `Encoding<-`("UTF-8")
#> [1] "<!DOCTYPE html>\n<html>\n\t<head>\n\t\t<meta charset=\"utf-8\">\n\t\t\n\n<meta name=\"viewport\" content=\"width=device-width, initial-scale=1\">\n\n<title>[討論] 林書豪如果加入馬刺能得到多少上場時間? - 看板 NBA - 批踢踢實業坊</title>\n<meta name=\"robots\" content=\"all\">\n<meta name=\"keywords\" content=\"Ptt BBS 批踢踢\">\n<meta name=\"description\" content=\"\n\n\n最近有傳言說林書豪可能會加入馬刺\n\n\">\n<meta property=\"og:site_name\" content=\"Ptt 批踢踢實業坊\">\n<meta property=\"og:title\" content=\"[討論] 林書豪如果加入馬刺能得到多少上場時間?\">\n<meta property=\"og:description\" content=\"\n\n\n最近有傳言說林書豪可能會加入馬刺\n\n\">\n<link rel=\"canonical\" href=\"https://www.ptt.cc/bbs/NBA/M.1463302851.A.8D7.html\">\n\n<link rel=\"stylesheet\" type=\"text/css\" href=\"//images.ptt.cc/v2.17/bbs-common.css\">\n<link rel=\"stylesheet\" type=\"text/css\" href=\"//images.ptt.cc/v2.17/bbs-base.css\" media=\"screen\">\n<link rel=\"stylesheet\" type=\"text/css\" href=\"//images.ptt.cc/v2.17/bbs-custom.css\">\n<link rel=\"stylesheet\" type=\"text/css\" href=\"//images.ptt.cc/v2.17/pushstream.css\" media=\"screen\">\n<link rel=\"stylesheet\" type=\"text/css\" href=\"//images.ptt.cc/v2.17/bbs-print.css\" media=\"print\">\n\n\n<script src=\"//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js\"></script>\n<script src=\"//images.ptt.cc/v2.17/bbs.js\"></script>\n\n\n\t\t\n\n<script type=\"text/javascript\">\n\n  var _gaq = _gaq || [];\n  _gaq.push(['_setAccount', 'UA-32365737-1']);\n  _gaq.push(['_setDomainName', 'ptt.cc']);\n  _gaq.push(['_trackPageview']);\n\n  (function() {\n    var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;\n    ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';\n    var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);\n  })();\n\n</script>\n\n\n\t</head>\n    <body>\n\t\t\n<div id=\"fb-root\"></div>\n<script>(function(d, s, id) {\nvar js, fjs = d.getElementsByTagName(s)[0];\nif (d.getElementById(id)) return;\njs = d.createElement(s); js.id = id;\njs.src = \"//connect.facebook.net/en_US/all.js#xfbml=1\";\nfjs.parentNode.insertBefore(js, fjs);\n}(document, 'script', 'facebook-jssdk'));</script>\n\n<div id=\"topbar-container\">\n\t<div id=\"topbar\" class=\"bbs-content\">\n\t\t<a id=\"logo\" href=\"/\">批踢踢實業坊</a>\n\t\t<span>&rsaquo;</span>\n\t\t<a class=\"board\" href=\"/bbs/NBA/index.html\"><span class=\"board-label\">看板 </span>NBA</a>\n\t\t<a class=\"right small\" href=\"/about.html\">關於我們</a>\n\t\t<a class=\"right small\" href=\"/contact.html\">聯絡資訊</a>\n\t</div>\n</div>\n<div id=\"navigation-container\">\n\t<div id=\"navigation\" class=\"bbs-content\">\n\t\t<a class=\"board\" href=\"/bbs/NBA/index.html\">返回看板</a>\n\t\t<div class=\"bar\"></div>\n\t\t<div class=\"share\">\n\t\t\t<span>分享</span>\n\t\t\t<div class=\"fb-like\" data-send=\"false\" data-layout=\"button_count\" data-width=\"90\" data-show-faces=\"false\" data-href=\"http://www.ptt.cc/bbs/NBA/M.1463302851.A.8D7.html\"></div>\n\n\t\t\t<div class=\"g-plusone\" data-size=\"medium\"></div>\n<script type=\"text/javascript\">\nwindow.___gcfg = {lang: 'zh-TW'};\n(function() {\nvar po = document.createElement('script'); po.type = 'text/javascript'; po.async = true;\npo.src = 'https://apis.google.com/js/plusone.js';\nvar s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s);\n})();\n</script>\n\n\t\t</div>\n\t</div>\n</div>\n<div id=\"main-container\">\n    <div id=\"main-content\" class=\"bbs-screen bbs-content\"><div class=\"article-metaline\"><span class=\"article-meta-tag\">作者</span><span class=\"article-meta-value\">magneto5566 (萬磁王5566_麥寮法斯賓達)</span></div><div class=\"article-metaline-right\"><span class=\"article-meta-tag\">看板</span><span class=\"article-meta-value\">NBA</span></div><div class=\"article-metaline\"><span class=\"article-meta-tag\">標題</span><span class=\"article-meta-value\">[討論] 林書豪如果加入馬刺能得到多少上場時間?</span></div><div class=\"article-metaline\"><span class=\"article-meta-tag\">時間</span><span class=\"article-meta-value\">Sun May 15 17:00:48 2016</span></div>\n\n\n最近有傳言說林書豪可能會加入馬刺\n\n不管對林書豪或對球迷來說馬刺都是個很棒的選擇\n\n馬刺今年例行賽戰績高達67勝,主力陣容維持的話明年應該依舊有60勝左右\n\n雖然波波維奇用兵如神,但林書豪在馬刺到底能獲得多少上場時間呢\n\n林書豪應該是替補PG和SG的位置\n\n單看馬刺和雷霆的系列賽\n\n馬刺的後場部分主要由4位球員分擔時間\n\n先發: Danny Green , Tony Parker\n\n替補: Manu Ginobili, Patty Mills\n\n\n理論上 林書豪最有機會的是Ginobili的位置\n\n畢竟鬼切已經38歲,下季會不會回來都還不確定\n\n林書豪的切入能力雖然沒有巔峰的鬼切犀利\n\n但是大勝38歲鬼切應該是沒問題\n\n相信波波維奇很了解這一點\n\n不知道大家怎麼看呢?\n\n\n--\n<span class=\"f2\">※ 發信站: 批踢踢實業坊(ptt.cc), 來自: 140.112.71.9\n</span><span class=\"f2\">※ 文章網址: <a href=\"https://www.ptt.cc/bbs/NBA/M.1463302851.A.8D7.html\" target=\"_blank\" rel=\"nofollow\">https://www.ptt.cc/bbs/NBA/M.1463302851.A.8D7.html</a>\n</span><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">sss1234     </span><span class=\"f3 push-content\">: 87分鐘</span><span class=\"push-ipdatetime\"> 05/15 17:02\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">h22212247888</span><span class=\"f3 push-content\">: 8.7分鐘</span><span class=\"push-ipdatetime\"> 05/15 17:02\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">rick        </span><span class=\"f3 push-content\">: 等七月再來分析好嗎?</span><span class=\"push-ipdatetime\"> 05/15 17:02\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">demonh311   </span><span class=\"f3 push-content\">: 當然是當基石</span><span class=\"push-ipdatetime\"> 05/15 17:02\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">arcss       </span><span class=\"f3 push-content\">: 前半年冰凍，後半年15分鐘/場</span><span class=\"push-ipdatetime\"> 05/15 17:03\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">hunt5566    </span><span class=\"f3 push-content\">: 呵呵 波波又藏招不讓豪鬼上囉</span><span class=\"push-ipdatetime\"> 05/15 17:04\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">Xenogamer   </span><span class=\"f3 push-content\">: 0</span><span class=\"push-ipdatetime\"> 05/15 17:04\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">love1500274 </span><span class=\"f3 push-content\">: Pop會讓書豪取代跑車先發 書豪會拿下年度mvp</span><span class=\"push-ipdatetime\"> 05/15 17:05\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">littlegreen </span><span class=\"f3 push-content\">: 馬刺需要切入沒錯 但是切傳能力 這書豪比較弱</span><span class=\"push-ipdatetime\"> 05/15 17:06\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">噓 </span><span class=\"f3 hl push-userid\">r30385      </span><span class=\"f3 push-content\">: 8.7秒</span><span class=\"push-ipdatetime\"> 05/15 17:08\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">donnylee    </span><span class=\"f3 push-content\">: Mills也差不多要退了，40歲</span><span class=\"push-ipdatetime\"> 05/15 17:12\n</span></div>         Mills 27歲而已\n<span class=\"f2\">※ 編輯: magneto5566 (140.112.71.9), 05/15/2016 17:14:25\n</span><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">darkfeather </span><span class=\"f3 push-content\">: 美媒建議變傳言，這進化速度還真快</span><span class=\"push-ipdatetime\"> 05/15 17:15\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">donnylee    </span><span class=\"f3 push-content\">: 喔，我記錯了，那是哪一個40？</span><span class=\"push-ipdatetime\"> 05/15 17:18\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">Mooooose    </span><span class=\"f3 push-content\">: Popo黑掉的所花的時間會比較多嗎?</span><span class=\"push-ipdatetime\"> 05/15 17:18\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">erotica     </span><span class=\"f3 push-content\">: 阿豪打1 2號都可以  還可以各種大小鎖防守</span><span class=\"push-ipdatetime\"> 05/15 17:21\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">噓 </span><span class=\"f3 hl push-userid\">king181239  </span><span class=\"f3 push-content\">: 去專版問啊</span><span class=\"push-ipdatetime\"> 05/15 17:21\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">king181239  </span><span class=\"f3 push-content\">: 他們會說超過35分鐘</span><span class=\"push-ipdatetime\"> 05/15 17:21\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">erotica     </span><span class=\"f3 push-content\">: 屌打上述4個人</span><span class=\"push-ipdatetime\"> 05/15 17:21\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">king181239  </span><span class=\"f3 push-content\">: 事實上只能出賽20幾</span><span class=\"push-ipdatetime\"> 05/15 17:22\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">噓 </span><span class=\"f3 hl push-userid\">s925407     </span><span class=\"f3 push-content\">: 怎麼會有人說Mills40歲啦，一日球迷也沒這麼不專業</span><span class=\"push-ipdatetime\"> 05/15 17:22\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">s925407     </span><span class=\"f3 push-content\">: 啦</span><span class=\"push-ipdatetime\"> 05/15 17:22\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">a10141013   </span><span class=\"f3 push-content\">: 馬刺大約20-25分鐘 然後popo被說冰箱</span><span class=\"push-ipdatetime\"> 05/15 17:24\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">dream1285201</span><span class=\"f3 push-content\">: 一個球員會黑掉大多跟他的球迷有關</span><span class=\"push-ipdatetime\"> 05/15 17:24\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">smtp        </span><span class=\"f3 push-content\">: 重點是馬刺想出多少爭取豪哥?</span><span class=\"push-ipdatetime\"> 05/15 17:28\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">kl015013    </span><span class=\"f3 push-content\">: 20</span><span class=\"push-ipdatetime\"> 05/15 17:29\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">bycarbird   </span><span class=\"f3 push-content\">: 0，因為書豪不是波波的菜</span><span class=\"push-ipdatetime\"> 05/15 17:30\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">MoMovincent </span><span class=\"f3 push-content\">: 那個說40歲的應該是要說a米吧</span><span class=\"push-ipdatetime\"> 05/15 17:30\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">s95115260   </span><span class=\"f3 push-content\">: 馬刺怎麼可能要球權的球員</span><span class=\"push-ipdatetime\"> 05/15 17:31\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">love1500274 </span><span class=\"f3 push-content\">: 他想說的是Miller 打成Mills  lol</span><span class=\"push-ipdatetime\"> 05/15 17:32\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">kiwi1220    </span><span class=\"f3 push-content\">: 40是 ，Miller</span><span class=\"push-ipdatetime\"> 05/15 17:33\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">miler22020  </span><span class=\"f3 push-content\">: 20分鐘 球權不多 然後popo從此黑掉</span><span class=\"push-ipdatetime\"> 05/15 17:36\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">scatology   </span><span class=\"f3 push-content\">: 5 垃圾時間</span><span class=\"push-ipdatetime\"> 05/15 17:36\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">smtp        </span><span class=\"f3 push-content\">: 10M簽的話, 上場時間不可能只有20分鐘...</span><span class=\"push-ipdatetime\"> 05/15 17:37\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">forker561   </span><span class=\"f3 push-content\">: 第一年不會有上場時間 最快第二年才有上場時間</span><span class=\"push-ipdatetime\"> 05/15 17:38\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">candy9999   </span><span class=\"f3 push-content\">: 去哪都比在黃蜂好</span><span class=\"push-ipdatetime\"> 05/15 17:40\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">DiAbLoE     </span><span class=\"f3 push-content\">: popo會變黑人</span><span class=\"push-ipdatetime\"> 05/15 17:41\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">smtp        </span><span class=\"f3 push-content\">: 豪哥今年曾說,年薪影響別人對你評價,可見企圖心很強</span><span class=\"push-ipdatetime\"> 05/15 17:41\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">happyalex   </span><span class=\"f3 push-content\">: 公道價8分鐘</span><span class=\"push-ipdatetime\"> 05/15 17:43\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">goury       </span><span class=\"f3 push-content\">: 千萬不要去馬刺...Linsanity的重點是明星度，而不是</span><span class=\"push-ipdatetime\"> 05/15 17:47\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">goury       </span><span class=\"f3 push-content\">: 馬刺這樣只在乎勝利，讓買票進場的人看不到球星的隊</span><span class=\"push-ipdatetime\"> 05/15 17:48\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">loverxa     </span><span class=\"f3 push-content\">: 到時不用豪神 就沒人在跟你用兵如神了啦</span><span class=\"push-ipdatetime\"> 05/15 17:49\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">crazywill   </span><span class=\"f3 push-content\">: 馬刺不會要阿豪 不用討論了</span><span class=\"push-ipdatetime\"> 05/15 17:50\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">birdman5656 </span><span class=\"f3 push-content\">: 先等波波帶完奧運吧</span><span class=\"push-ipdatetime\"> 05/15 17:51\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">yyyyy       </span><span class=\"f3 push-content\">: 馬刺應該以我豪為核心進行重建才對</span><span class=\"push-ipdatetime\"> 05/15 17:53\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">leocheng    </span><span class=\"f3 push-content\">: 馬刺喜歡跳投好的 怎麼可能愛豪鬼</span><span class=\"push-ipdatetime\"> 05/15 18:04\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">june0204    </span><span class=\"f3 push-content\">: 還是2000找康利吧</span><span class=\"push-ipdatetime\"> 05/15 18:12\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">HowWhy99    </span><span class=\"f3 push-content\">: 8.7分 不能再多了</span><span class=\"push-ipdatetime\"> 05/15 18:12\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">crazylin924 </span><span class=\"f3 push-content\">: 35分鐘 （一整季</span><span class=\"push-ipdatetime\"> 05/15 18:19\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">噓 </span><span class=\"f3 hl push-userid\">xman262     </span><span class=\"f3 push-content\">: 487秒</span><span class=\"push-ipdatetime\"> 05/15 18:24\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">噓 </span><span class=\"f3 hl push-userid\">ppo7741     </span><span class=\"f3 push-content\">: 8.7分，跟這篇文的分數一樣，不能再高了</span><span class=\"push-ipdatetime\"> 05/15 18:25\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">carey1119   </span><span class=\"f3 push-content\">: 8.7分鐘</span><span class=\"push-ipdatetime\"> 05/15 18:33\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">DurantKevin </span><span class=\"f3 push-content\">: 。。。</span><span class=\"push-ipdatetime\"> 05/15 18:34\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">qq1029qq    </span><span class=\"f3 push-content\">: 87分鐘無誤</span><span class=\"push-ipdatetime\"> 05/15 18:40\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">drew9992    </span><span class=\"f3 push-content\">: <a href=\"http://i.imgur.com/0XBGyQU.jpg\" target=\"_blank\" rel=\"nofollow\">http://i.imgur.com/0XBGyQU.jpg</a></span><span class=\"push-ipdatetime\"> 05/15 19:01\n</span></div><div class=\"richcontent\"><img src=\"//i.imgur.com/0XBGyQU.jpg\" alt=\"\" /></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">dai26       </span><span class=\"f3 push-content\">: 若能完全取代馬妞,大概30分鐘，而且可打滿第四節</span><span class=\"push-ipdatetime\"> 05/15 19:20\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">vicyong     </span><span class=\"f3 push-content\">: 不要在幻想了</span><span class=\"push-ipdatetime\"> 05/15 19:23\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">gotohikaru  </span><span class=\"f3 push-content\">: 第一年不用想</span><span class=\"push-ipdatetime\"> 05/15 19:32\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">waw20002002 </span><span class=\"f3 push-content\">: 8.7分鐘！不能在多了</span><span class=\"push-ipdatetime\"> 05/15 20:13\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">噓 </span><span class=\"f3 hl push-userid\">an565an565  </span><span class=\"f3 push-content\">: 後衛來馬刺都要被冰一整季</span><span class=\"push-ipdatetime\"> 05/15 21:07\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">trylovetom  </span><span class=\"f3 push-content\">: Parker不是被豪哥哥電？</span><span class=\"push-ipdatetime\"> 05/15 21:09\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">smtp        </span><span class=\"f3 push-content\">: Parker是輸在年紀, 巔峰時不可能會被豪哥電~</span><span class=\"push-ipdatetime\"> 05/15 21:12\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">噓 </span><span class=\"f3 hl push-userid\">Yginger1    </span><span class=\"f3 push-content\">: 42分鐘 全場打好打滿</span><span class=\"push-ipdatetime\"> 05/15 21:19\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">pickoff     </span><span class=\"f3 push-content\">: 馬刺不收。問下一隊謝謝</span><span class=\"push-ipdatetime\"> 05/15 21:22\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">mmshlovebob </span><span class=\"f3 push-content\">: 8.7分鐘 不能再多了</span><span class=\"push-ipdatetime\"> 05/15 21:36\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">roc074      </span><span class=\"f3 push-content\">: 8.7時</span><span class=\"push-ipdatetime\"> 05/15 22:04\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">噓 </span><span class=\"f3 hl push-userid\">deathgale   </span><span class=\"f3 push-content\">: 等加盟了再來討論，記者都自以為球團老闆...</span><span class=\"push-ipdatetime\"> 05/15 22:38\n</span></div><div class=\"push\"><span class=\"hl push-tag\">推 </span><span class=\"f3 hl push-userid\">squall410339</span><span class=\"f3 push-content\">: 快去啦馬刺黑掉就是爽</span><span class=\"push-ipdatetime\"> 05/15 23:29\n</span></div><div class=\"push\"><span class=\"f1 hl push-tag\">→ </span><span class=\"f3 hl push-userid\">raku        </span><span class=\"f3 push-content\">: 一開始一場應該是不到10分鐘...</span><span class=\"push-ipdatetime\"> 05/16 00:34\n</span></div></div>\n    \n    <div id=\"article-polling\" data-pollurl=\"/poll/NBA/M.1463302851.A.8D7.html?cacheKey=2052-14787853&offset=7844&offset-sig=05b0d881a2af63a68de9ce2d0f1cda56eec2d548\" data-longpollurl=\"/v1/longpoll?id=5ef93f8aa82d4cf930eb27310d147571cf13936a\" data-offset=\"7844\"></div>\n    \n\n    \n</div>\n\n    </body>\n</html>\n"

auto parsed
httr provides a number of default parsers for common file types:
html_document, csv, json, jpeg, png. See ?httr::content

content(res, "parsed")
#> {xml_document}
#> <html>
#> [1] <head>\n\t\t<meta charset="utf-8"/>\n\t\t\n\n<meta name="viewport" c ...
#> [2] <body>\n\t\t\n<div id="fb-root"/>\n<script><![CDATA[(function(d, s,  ...

Beware of System Encoding

Parse data with appropriate encoding
Use Encoding(), iconv() and Sys.setlocale() in Windows (non-UTF8 system).
iconvlist() to show all encodings availabe.

Encoding

?Encoding ?iconv

Unix-like

## check out your system locale
Sys.getlocale()
#> [1] "en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8"
aa <- "你好嗎"
Encoding(aa)
#> [1] "UTF-8"
charToRaw(aa)
#> [1] e4 bd a0 e5 a5 bd e5 97 8e

(aa_big5 <- iconv(aa, from = "UTF-8", to = "Big5"))
#> [1] "\xa7A\xa6n\xb6\xdc"
Encoding(aa_big5)
#> [1] "unknown"
harToRaw(aa_big5)
#> [1] a7 41 a6 6e b6 dc

Windows

# On Windows
Sys.getlocale()
#> "CP950"
aa <- "你好嗎"
Encoding(aa)
#> "unknown"
aa_utf8 <- iconv(aa, from = "Big5", to = "UTF-8")
Encoding(aa_utf8)
#> "UTF-8"

The secret of URL

URL?par1=val1&par2=val2

The query string is sent in the URL of a GET request
Non-ASCII character and some preserved characters need to be encoded with URL Encode
In most situation, you may need to manipulate the query string when you write a crawler

Query String

You can assign query parameter with query()

res1 <- GET(
  "http://ecshweb.pchome.com.tw/search/v3.3/all/results?q=sony&page=1&sort=rnk/dc"
)

url2 <- "http://ecshweb.pchome.com.tw/search/v3.3/all/results"
res2 <- GET(url2,
           query = list(q="sony", page="1", sort="rnk/dc"))
identical(res1$content, res2$content)

#> [1] TRUE

Url Encoding in R

URLencode(" ")

#> [1] "%20"

greeting = "你好嗎我很好"
greeting_enc = URLencode(greeting)
greeting_enc

#> [1] "%E4%BD%A0%E5%A5%BD%E5%97%8E%E6%88%91%E5%BE%88%E5%A5%BD"

URLdecode(greeting_enc)

#> [1] "你好嗎我很好"

Concatenate strings / String formatting

paste0("hihi", greeting)

#> [1] "hihi你好嗎我很好"

paste0("hihi", greeting, 1:3)

#> [1] "hihi你好嗎我很好1" "hihi你好嗎我很好2" "hihi你好嗎我很好3"

paste("hihi", greeting, 1:3, sep = " ", collapse = ",")

#> [1] "hihi 你好嗎我很好 1,hihi 你好嗎我很好 2,hihi 你好嗎我很好 3"

sprintf("%s,%s嗎?", "hihi", greeting)

#> [1] "hihi,你好嗎我很好嗎?"

What to Parse

結構化資料

html elements: (rvest::html_node)
json, jsonp: PChome, 紫外線即時監測資料 (jsonlite::fromJSON)
html table: 公開資訊觀測站 (rvest::html_table, XML::readHtmlTable)
xml table: 7-11 (XML::xmlToDataFrame)

非結構化資料

RegEx: 7-11 的 citycode (areacode.js)、東森房屋

Parsing Response Content: Text Type

rvest

A web scraper designed to work with magrittr.

Create a html document with read_html()
Select parts of a document using css selectors or xpath
- html_nodes(doc, css = "<css selector>")
- html_nodes(doc, xpath = "<css selector>")
Extract components with
- html_name(): the name of the tag
- html_text(): all text inside the tag
- html_attr(): contents of a single attribute
- html_attrs(): all attributes
- html_table: parse tables into data frames

Use with rvest

起手式

GET(url) %>% content(as="text") %>% rvest::read_html()

Extract elements from HTML document

Tree Structure of HTML (Document Object Model, DOM)

<a href = "www.meetup.com/Taiwan-R">
  Taiwan R User Group Website
</a>

nodename : a
attribute : href with value "www.meetup.com/Taiwan-R"
text: Taiwan R User Group Website

Extract with css

CSS practice
http://flukeout.github.io/

doc <- read_html("http://leoluyi.github.io/RCrawler101_201605_Week2/resources/data/demo.html")
doc %>% 
    html_nodes(css = ".character") %>% 
    html_text

#> [1] "\n            data-sci.info\n        "         
#> [2] "\n            Number:\n            2\n        "

doc %>% 
    html_nodes(css = "#title > .link") %>% 
    html_text

#> [1] "data-sci.info"

Extract with xpath

doc <- read_html("http://leoluyi.github.io/RCrawler101_201605_Week2/resources/data/demo.html")
doc %>% 
    html_nodes(xpath = "//*[@class='character']") %>% 
    html_text

#> [1] "\n            data-sci.info\n        "         
#> [2] "\n            Number:\n            2\n        "

doc %>% 
    html_nodes(xpath = "//div[@id='title']/a") %>% 
    html_text

#> [1] "data-sci.info"

Extract name of tag

node = doc %>% 
    html_nodes(css = "#summary") %>% 
    html_name
node

#> [1] "div"

Extract link

link = doc %>% 
    html_nodes(xpath = "/html/body/div[@id='title']/a") %>%
    html_attr("href")
link

#> [1] "http://data-sci.info/r-crawler-101/"

Example: PTT

use package xmlview to parse XML content and extract elements.

Extract table

rvest::html_table
(rvest::html_table is temperarily not working with unicode data on Windows.)

students <- read_html("http://leoluyi.github.io/RCrawler101_201605_Week2/resources/data/demo.html") %>% 
    html_nodes(css = "#table1>table") %>%
    html_table()
students

#> [[1]]
#>    Name Gender Age
#> 1 Alice Female  24
#> 2  Jane Female  26

Extract table

XML::readHTMLTable()

res_text <- GET("http://leoluyi.github.io/RCrawler101_201605_Week2/resources/data/demo.html") %>% 
  content("text", encoding = "UTF-8") %>% 
  `Encoding<-`("UTF-8")

# create `HTMLInternalDocument` for following use
doc <- XML::htmlParse(res_text, encoding = "UTF-8")
class(doc)

#> [1] "HTMLInternalDocument" "HTMLInternalDocument" "XMLInternalDocument" 
#> [4] "XMLAbstractDocument"

# Parse tables with XML::readHTMLTable()
tables <- XML::readHTMLTable(doc)

# Or you can read table from a html string
tables2 <- res_text %>% XML::readHTMLTable(encoding = "UTF-8")
identical(tables, tables2)

#> [1] TRUE

str(tables) # take a look 
View(tables[[2]]) # take a look

Result

姓名	年齡
白素貞	15
聶小倩	32
祝英台	54

Example: Yahoo Stock

Yahoo Stock

Example: 公開資訊觀測站

公開資訊觀測站

Parse XML table

Parse XML table with XML::xmlToDataFrame()

Example

Seven Eleven
RegEx: 7-11 citycode (areacode.js)

Parse JSON format

Yun can parse JSON with jsonlite in R

Parse JSON with `jsonlite`

Example: PChome API

library(jsonlite)
library(magrittr)
res <- GET("http://ecshweb.pchome.com.tw/search/v3.3/all/results?q=sony&page=1&sort=rnk/dc")

jsonlite::fromJSON()

res_df <- content(res, as = "text", encoding = "UTF-8") %>% 
  fromJSON() %>%
  .$prods  # equivelent to (function(x) {x$prods})

str(res_df)

`httr` auto parse json as list

res_list <- content(res, as = "parsed")
# str(res_list)
res_list$prods[[1]]

Combind list of dataframes with loop (not recommended)

# str(res_list$prods)
res_df2 = data.frame()
for (i in 1:length(res_list$prods)) {
  res_df2 = rbind(res_df2, 
                  data.frame(res_list$prods[[i]], 
                             stringsAsFactors = FALSE))
}
identical(res_df, res_df2)

More general way to combine list of dataframes

do.call + rbind
data.table::rbindlist

Parse Parse list of data.frames with `do.call` + `rbind`

res_df3 = data.frame(do.call(rbind, res_list$prods))
identical(res_df, res_df3)

# An ugly data.frame
str(res_df3)

非結構化資料解析: Regular Expression

Package: stringr - str_replace(), str_replace_all() - str_extract(), str_extract_all()

library(stringr)
fruits <- c("one apple", "two pears", "three bananas")
str_replace(fruits, "[aeiou]", "-")
#> [1] "-ne apple"     "tw- pears"     "thr-e bananas"
str_replace_all(fruits, "[aeiou]", "-")
#> [1] "-n- -ppl-"     "tw- p--rs"     "thr-- b-n-n-s"

shopping_list <- c("apples x4", "bag of flour", "bag of sugar", "milk x2")
str_extract(shopping_list, "[a-z]+")
#> [1] "apples" "bag"    "bag"    "milk"
str_extract_all(shopping_list, "[a-z]+")
#> [[1]]
#> [1] "apples" "x"     
#> 
#> [[2]]
#> [1] "bag"   "of"    "flour"
#> 
#> [[3]]
#> [1] "bag"   "of"    "sugar"
#> 
#> [[4]]
#> [1] "milk" "x"

Exercise : 東森房屋

東森房屋
試著找到「新北市」的資料

Exercise: 紫外線即時監測資料

行政院環境保護署環境資源資料開放平台提供了一系列的RESTful Api供大家取用，請試著把紫外線即時監測資料的資料取回來並轉成data.frame

Save your data

write.csv: write data.frame as csv file
download.file: save html, jpeg, etc
writeBin: write binary object into disk
RSQLite: SQLite connector in R

write.csv

library(jsonlite)
library(httr)
url = "http://ecshweb.pchome.com.tw/search/v3.3/all/results?q=sony&page=1&sort=rnk/dc"
res_df = GET(url) %>% 
    content(res, as = "text") %>% 
    fromJSON() %>% 
    .$prods     # equivelent to (function(x) {x$prods})
write.csv(res_df, "resources/data/pchome.csv", row.names = FALSE)

download.file

To download a file from the Internet. download.file takes advantage of internet utilities such as curl or wget and may fail if you don’t have any of these utilities in your system.

dest_dir = "resources/data/download"
dir.create(dest_dir, showWarnings = FALSE, recursive = TRUE)

# Download whole HTML file
download.file("https://www.r-project.org/", 
              file.path(dest_dir, "r-project.org.html"))

# Download image
download.file("https://www.r-project.org/Rlogo.png",
              file.path(dest_dir, "Rlogo.png"))

list.files(dest_dir)

writeBin

To write binary data to your local disk.

r = GET("http://opendata.epa.gov.tw/webapi/api/rest/datastore/355000000I-000004/?format=json")
# Set as = "raw" to prevent any character encoding
bin = content(r, as = "raw")
writeBin(bin, "resources/data/download/uv.json")

Database

RSQLite: A light-weight database engine interface in R
- PChome Example
Other relational database connector in R
- RODBC
- RJDBC
- RMySQL
- …

RCrawler101-201605 (Week2)

How to use this slides

Outline

Install: Chrome Extension

Recap Observation Skills and HTTP request for Connection

R Packages Required

Pipeline Coding

Crawler’s toolkits in R

misc

Install Packages

(if you haven’t installed those packages yet)

Let’s Rock with R!

Hello RStudio

RStudio Settings

Must-known keyboard shortcuts

R recap

How to get help

Working Environment

Basic Data Structure

(Atomic) Vector

List

Visualising lists

Lists Subsetting

Lists Subsetting (Pepper Shaker)

Data Frame

Recap: data structure

Function

Function in R

Control Flow

If

for

tryCatch

magrittr

What is magrittr

Example

Workflow of Crawler Design

Architecture of Crawlers

Workflow

Crawler’s toolkits in R

Web Connector in R

HTTP request

Web Connector in R

httr

Connection: GET Method

起手式

一個例子學會第一隻爬蟲

Cookies

The response status code

Connection: POST method

起手式

一個例子學會第二隻爬蟲: Guestbook

Exercise: Guestbook

Set header

Let’s see what we got in theresponse body

The Response Body

The Response Body: httr::content()

Beware of System Encoding

Encoding

The secret of URL

Query String

Url Encoding in R

Concatenate strings / String formatting

Parsing Data

What to Parse

結構化資料

非結構化資料

Parsing Response Content: Text Type

rvest

Use with rvest

Extract elements from HTML document

Tree Structure of HTML (Document Object Model, DOM)

A simple HTML document

Create HTML document object

Extract with css

Extract with xpath

Extract name of tag

Extract link

Example: PTT

Extract table

Extract table

Let’s see what we got in the
response body

The Response Body: `httr::content()`

Parse JSON with `jsonlite`

`httr` auto parse json as list

Parse Parse list of data.frames with `do.call` + `rbind`